Layer and devlopment

1. Introduction
 Retina, the innermost tunic of the eyeball.
 It is a thin delicate & transparent membrane.
 Its thickness:
◦ At the posterior pole in the peri-papillary region is approximately
0.56mm
◦ At the equator 0.18 to 0.2mm
◦ At the ora serrata approx. 0.1mm
 It is the most highly developed tissue of the eye.
 It appears purplish-red due to visual purple of the rods.
 After death, the retina appears white opaque.

2. Gross Anatomy
 Retina extends
from the optic
disc to the ora
serrata & has a
surface area of
about 266sq.mm

3. Gross Anatomy
 Grossly on ophthalmoscopic examination it can
be divided into 3 distinct regions:
1) Optic disc
2) Macula lutea
3) Peripheral retina

4. Optic Disc
 It is a pale pink, well-defined circular
area of about 1.5mm diameter.
 “At the optic disc, all the retinal layers
terminate except the nerve fibre layer”,
which pass through the lamina cribrosa
to run into the optic nerve.
 In comparison to the rest of retina, the
optic disc appears white d/t lamina
cribrosa and medullated nerve fibres
behind it & absence of vascular choroid.

5. Optic Disc
 In the centre, where the nerve fibres are thinnest, the
white lamina shines more brightly.
 The grey spot in the lamina are d/t to the non-
medullated nerve fibres reflecting less light than the
white connective tissue fibres.
 The physiological cup of the optic disc is a depression
seen in it.The central retinal vessels emerge through
the centre of this cup.
 Increase in the size of the cup & difference in the size of
cup of two eyes should be watched suspiciously to rule
out glaucoma.

6. Macula lutea
 The macula lutea (yellow spot) is a
comparatively dark area 5.5mm in diameter,
situated at the posterior pole of the eyeball,
temporal to the optic disc.
 Horizontally ellipsed area demarcated
approx. by the upper and lower arcuate &
temporal retinal vessels.
 It corresponds to approx. 15 degree of the
visual field and that photopic vision and
colour vision are primarily functions of this
area.

7. Macula lutea
 It consists of the following parts:
1) Fovea centralis (fovea)
2) Foveola
3) Umbo
4) Foveal avascular zone (FAS)
5) Parafoveal area
6) Perifoveal area

8. Fovea centralis / Fovea
 Central depressed
part of the macula.
 1.85mm in
diameter &
0.25mm in
thickness
 It corresponds to 5
degree of visual
field & is most
sensitive part of the
retina.

9. Foveola
 0.35mm in diameter.
 Forms the central
floor of the fovea.
 It is situated about 2
disc diameter (3mm)
away from the
temporal edge of the
optic disc & about
1mm below the
horizontal meridian.

10. Umbo
 Tiny depression in
the center of the
foveola which
corresponds to the
ophthalmoscopically
visible foveolar
reflex, seen in most
normal eyes.
 Loss of the foveolar
reflex may be an
early sign of
damage.

11. Foveal Avascular Zone
 Located inside the fovea but outside the
foveola.
 Its exact diameter is variable and its
location can be determined with
accuracy only by fluorescein
angiography.

12. Parafoveal Area
 The parafovea is a
belt that measures
0.5 mm in width
and surrounds the
foveal margin.

13. Perifoveal Area
 The perifovea
surrounds the
parafovea as a belt
that measures 1.5
mm wide

14. Peripheral Retina
 It can be divided into 4 regions:
1) Near periphery
2) Mid periphery
3) Far periphery
4) Ora serrata

15. Peripheral Retina
 Near periphery:
◦ Refers to circumscribed region of about
1.5mm around the macula.
 Mid periphery:
◦ Occupies a 3mm wide zone around the near
periphery.
 Far periphery:
◦ It extends from optic disc 9-10mm on the
temporal side & 16mm on the nasal side in
the horizontal meridian.

16. Peripheral Retina
 Ora serrata:
◦ It is the serrated peripheral margin where
the retina ends & ciliary body starts.
◦ At the ora, the sensory retina is firmly
attached both to the vitreous & pigmented
epithelium.
◦ 2.1mm wide temporally & 0.7-0.8mm wide
nasally
◦ Its distance from the limbus is 6.0mm
nasally & 7.0mm temporally.
◦ It is located 6-8mm away from the equator
& 25mm from the optic nerve on the nasal
side.

17. Microscopic Structure Of The
Retina
 Retina consist of three types of cells & their synapses
arranged in the following layers (from outwards to
inwards):
1) Retinal pigment epithelium
2) Layers of rods & cones
3) External limiting membrane
4) Outer nuclear layer
5) Outer molecular (plexiform) layer
6) Inner nuclear layer
7) Inner molecular (plexiform) layer
8) Ganglion cell layer
9) Nerve fiber layer
10) Internal limiting membrane

19. Retinal Pigment Epithelium
(RPE)
 Outermost layer of retina.
 Consist of a single layer of hexagonal-shaped
cells containing pigment.
 The RPE cells shows fine mottling d/t unequal
pigmentation of the cell & this is responsible for
granular appearance of the fundus.
 RPE is firmly adherent to the underlying
BRUCH’S MEMBRANE (basal lamina of the
choroid) & loosely attached to the layer of rods &
cones.

20. Retinal Pigment Epithelium
 The potential space between RPE & the sensory
retina is c/d SUBRETINAL SPACE.
 A separation of the RPE from the sensory retina
is c/d RETINAL DETACHMENT,& the fluid
between the two layers is c/d SUB RETINAL
FLUID (SRF)
 Splitting of the retina at the level of the outer
plexiform layer is cld SENILE RETINOSCHISIS.
 Splitting of the retina in the nerve fibre layer with
the development of nerve fibre layer break is c/d
JUVENILE RETINOSCHISIS.

21. Retinal Pigment Epithelium
 Adjacent RPE cells are
connected to each other by
tight junctions (zonulae
occludens & zonulae
adherens) & constitute the
outer BLOOD-RETINAL
BARRIER.
 The RPE cells at the fovea
are taller, thinner & contains
more & large granules than
elsewhere in the fundus,
thereby giving a dark colour
to this area.
 The optical part of RPE is
formed by the microvilli which
project b/w the rods & cones
processes.
Apical surface of human retinal pigment
epithelium as seen through a scanning electron
microscope. Fine microvilli cover the surface and
reach up between the photoreceptor outer
segments (which have been peeled away in this
view).

22. Retinal Pigment Epithelium
 Functions:
◦ Play important role in photoreceptor renewal &
recycling of vitamin-A
◦ Maintains integrity of subretinal space by forming outer
blood-retinal barrier & actively pumping ions & water
out of this.
◦ Transport of nutrients & metabolites.
◦ Provides mechanical support to the processes of
photoreceptors & maintenance of retinal adhesion.
◦ They manufacture pigments which presumably has an
optical function in absorbing scattered light.
◦ Synthesis of growth factors to modulate adjacent
structures.
◦ Phagocytosis and digestion of photoreceptor wastes.
◦ Electrical homeostasis.
◦ Regeneration and repair after injury or surgery.

23. Mechanism of serous detachment. When the retinal pigment epithelium (RPE) is normal, no serous
detachment occurs beyond a focal site of leakage. When the RPE is compromised by choroidal or RPE
disease that impairs outward fluid transport, a serous detachment forms until absorption across the
exposed RPE balances the inward leak.

24. Layer Of Rods & Cones
 Rods contains a photosensitive substance visual
purple (rhodopsin ) & subserve the peripheral
vision (scotopic vision).
 Cones responsible for highly discriminatory central
vision (photopic vision) & colour vision.
 Rods are about 120 million & cones are about 6.5
million in number.
 The highest density of cones is at fovea with an
average of 199000 cones/sqmm
 The number of cones fall off rapidly outside the
fovea.

25. Layer Of Rods & Cones
 Cones density is 40-45% greater on the nasal
than on the temporal aspect of the retina, &
slightly lower in the superior than the inferior
retina at the mid periphery.
 Rods are absent at the fovea in an area of
0.35mm (Rod-free Zone) which corresponds to
1.25 degree of the visual field. They are
maximum below the optic disc (170,000/sq.mm)
& their number reduces towards the periphery.
 The entire nasal retina has 20-25% more rods
than does temporal retina, & the superior retina
has 2% more than the inferior retina.

26. Structure Of The
Photoreceptor
 Each photoreceptor consists of:
a) A cell body & nucleus (which lies in
the outer nuclear layer)
b) A cell process that extends into outer
plexiform layer
c) Inner & outer segment (which forms
the layer of rods & cones) .

27. The Rod Cell
 40-60 micro meter long
 Outer segment of the rod
is cylindrical, highly
refractile & contains visual
purple.
 It is composed of
numerous lipid protein
lamellar discs stacked
one on the top of the
other & surrounded by a
cell membrane. The disc
contain 90% of the visual
pigment.
 The number of discs
varies from 600-1000/rod.
Outer segment

28. The Rod Cell
 The inner segment of
the rod is thicker than
the outer segment. It
consist of 2 regions:
1) Ellipsoid (the outer
portion) is adjacent to
the outer segment &
contains abundant
number of
mitochondria.
2) Myoid (the inner
portion) contains the
glycogen as well as
the usual organelles.
Inner segment

29. The Rod Cell
 An outer rod fibre
arises from the inner
end of rod, which
passes through the
external limiting
membrane & swells
into a densely staining
nucleus - the rod
granule (which lies in
the outer nuclear
layer) & then
terminates as inner
rod fibre which at its
end has an end bulb
c/d the rod spherule
that is in contact with
the cone foot.

30. The Cone Cell
 40-80 micro meter
long. Largest at the
fovea (80micro meter)
& shortest at the
periphery (40micro
meter).
 The outer segment is
conical in shape,
much shorter than that
of rod & contains the
iodopsin.
 There are about 1000-
1200 disc/cone.

31. The Cone Cell
 The cone inner segment
& cilium are similar to the
rod structures, however
the cone ellipsoid is very
plump & contains a large
number of mitochondria.
 Outer fibre is absent. A
stout cone inner fiber
runs from the nucleus
which at the end is
provided with lateral
processes c/d cone foot
or cone pedicle (which
lies in the outer plexiform

32. The Interphotoreceptor Matrix (IPM)
& Interphotorecepter Retinoid
Binding Protein (IRBP)
 The IPM occupies the space between the
photoreceptor outer segments & the retinal
pigment epithelium.
 It is a complex structure consisting of
proteins, glycoproteins, GAGs &
proteoglycans such as chondroitin sulphate.
 The IPM has diverse range of functions,
including retinal attachment & adhesin
molecular trafficking, facilitation of
phagocytosis & probably photoreceptor outer
segment alignment.

33. The Interphotoreceptor Matrix
(IPM) & Interphotorecepter
Retinoid Binding Protein (IRBP)
 IRBP accounts for 70% of the soluble protein in
the IPM.
 IRBP is produced mainly by the cones.
 FUNTIONS OF IRBP:
1) Transport of retinoid between the photoreceptor
& the retinal pigment epithelium.
2) Minimize fluctuations in retinoid availability .
3) Protect the plasma membrane from the
damaging effect of high retinoid concentration.

34. External Limiting Membrane
 In low magnification, it appear as a
fenesterated membrane extending from
the ora serrata to the edge of the optic
disc; through which pass processes of
the rods & cones.
 Actually it is formed by the junctions
(zonulae adherentes) between the cell
membrane of photoreceptors & Muller’s
cells ( & thus it is not a basement
membrane) .

35. Outer Nuclear Membrane
 Formed by the nuclei of rods & cones.
 Rod nuclei forms the bulk of this multilayered outer
nuclear layer except in the cone dominated foveal
region.
 The number of rows of nuclei & thickness of this layer
varies from region to region are as follows:
Nasal to the disc: 8-9 layers of nuclei & 45 micro meter
thickness.
Temporal to disc: 4 rows of nuclei & 22 micro meter
thickness.
Foveal region: 10 rows of nuclei & 50 micro meter
thickness.
Rest of the retina except ora serrata: one row of cone
nuclei & 4 rows of rod nuclei with a thickness of 27 micro
meter.

36. Outer Plexiform Layer
 This layer contains the synapses between the
rod spherule & cone pedicles with the
dendrites of the bipolar cells & processes of
the horizontal cells.
 It marks the junction of the end organ of
vision & first order neurons in the retina.
 It is thickest at the macula (51 micro meter) &
consist predominately of oblique fibers that
have deviated from the fovea & is also known
as HENLE’S LAYER.

38. Inner Nuclear Layer
 It is thinner as compared to the outer
nuclear layer.
 This layer disappears at fovea & in the
rest of the retina consist of following:
a) Bipolar cells
b) Horizontal cells
c) Amacrine cells
d) The soma of the muller’s cells
e) Capillaries of the central retinal vessels

39. Bipolar Cells (Neurons)
 These are the neurons of first order of vision. They are
connected to the rods & cones by their dendrites & to the
ganglion cells by their axons..
 On the basis of morphology & synaptic relationship, nine
types of bipolar cells are seen under light microscopy:
1) Rod bipolar cell
2) Invaginating midget bipolar cells
3) Flat midget bipolar cells
4) Invaginating diffuse bipolar cells.
5) Flat diffuse bipolar cells.
6) On-centre blue cone bipolar cells.
7) Off – centre blue cone bipolar cells.
8) Giant bistratified bipolar cells.
9) Giant diffuse bipolar cells.

40. Horizontal Neurons
 These are flat cells & they connect rods
& cones with bipolar cells. They are of
two types:
◦ The type A horizontal cells have seven
groups of dendrites, which have contact with
triad of seven cone pedicles & their single
axon has contact with distant cone triad.
◦ The type B horizontal cells dendrites have
contact with rod receptors only & their axons
with the distant rod cells.

41. Amacrine Cells
 Situated within the innermost part of
inner nuclear layer.
 They connect the axons of the bipolar
cells to the dendrites & soma of the
ganglion cells, thus they are similar in
function to the horizontal cells.

42. Muller’s Cell
 Their nuclei & cell bodies lie within the inner
nuclear layer. Fibres from their outer ends extend
upto external limiting membrane & those from
their inner ends reach upto the internal limiting
membrane.
 The muller’s cell provide structural support &
contribute to the metabolism of the sensory
retina.
 Fibres from the Muller’s cell & cell membrane of
photoreceptors together constitute the external
limiiting membrane.
 In outer & inner nuclear layer, Muller’s cell
provide reticulum around the cell somata.
 In nerve fibre layer their processes interweave
with axons of ganglion cells.
 Fibres of the Muller’s cell takes part in the

43. Other Glial Cells
 In addition to Muller’s cell , the retina
contains other glial cells:
Astrocytes .
Microglia.
Oligodendrocytes.
 The astrocytes are most abundant &
are located around the blood vessels.

44. Inner Plexiform Layer
 It consists of
synapses between
the axon of bipolar
cells (first order
neuron), dendrites of
ganglion cells
(second order
neuron), & the
processes of
integrative amacrine
cells.
 This layer is absent
at the foveola.

45. Ganglion Cell Layer
 The cell bodies & the nuclei of the
ganglion cells lie in this layer.
 It is absent at the foveola.
 Ganglion cells have been variously
classified few classification are as follow:
1) W,X,& Y ganglion cells
2) P (P1 & P2 )& M GANGLION cells.
3) OFF-centre & ON- centre ganglion cells.
4) Monosynaptic & polysynaptic ganglion
cells.

46. Nerve Fibre Layer (Stratum
opticum)
 It consists of the unmyelinated axons of
the ganglion cells which converge at the
optic nerve head , pass through lamina
cribrosa & become ensheathed by
myelin posterior to lamina.
 This layer also contains:
◦ Centrifugal nerve fibres.
◦ Processes of Muller’s cell.
◦ Neuroglial cells.
◦ Retinal vessels.

47. Features Of Nerve Fibres
 Non-myelinated.
 Thickness 0.5 to 2 micro meter.
 Cytoplasm of the axons contains
microtubules, fine fibrils, mitochondria,
& occasional vesicles.

48. Arrangement Of Nerve Fibres In
The Retina
 Fibres from the nasal half
of the retina come directly
to the optic disc as
superior & inferior
radiating fibres (srf & irf ).
 Fibres from the macular
region pass straight in the
temporal part of the disc
as papillomacular bundle
(pmb).
 Fibres from the temporal
retina arch above & below
the macular &
papillomacular bundle as
superior & inferior arcuate
fibres (saf & iaf) with a

49. Arrangement OF Nerve Fibres
Of The Optic Nerve Head
 Fibres from the peripheral part of retina lie
deep in the retina, but occupy the most
peripheral (superficial) part of the optic disc.
 While the fibres originating closer to the optic
nerve head lie superficially in the retina &
occupy a more central (deep) portion of the
disc.

50. Thickness Of Nerve Fibre Layer
At The Disc
 Thickness of the RNFL around the
different quadrants of the optic disc
margin progressively increases in the
follwing order:
Most temporal/lateral quadrant (thinnest).
Upper temporal & lower temporal
quadrant.
Most medial quadrant .
Upper nasal & lower nasal quadrant
(thickest)

51. Clinical Significance Of Distribution &
Thickness Of Nerve Fibres At The Optic
Disc Margin
 Papilloedema appears first in the thickest
quadrant (upper nasal & lower nasal) &
last in the thinnest quadrant (most lateral ).
 Arcuate nerve fibre which occupy the
superior temporal & inferior temporal
quadrant of optic nerve head are most
sensitive to glaucomatous damage.
 Macular fibre are most resistant to
glaucomatous damage & explain the
retention of the central vision till end.

52. Internal Limiting Membrane
 It consists of:
A PAS (+)ve true basement membrane
(unlike ELM) that forms the interface b/w
retina & vitreous.
Collagen fibrils.
Proteoglycans (mostly hyaluronic acid) of
the vitreous.
Plasma membrane of the muller cells &
other glial cells of the retina.

53. Blood Supply Of The Retina
 ARTERIAL SUPPLY:
Outer 4 layers upto outer nuclear layer: from
choriocapillaris.
6 inner layers: from central retinal artery.
Outer plexiform layer gets its blood supply from the
central retinal artery & partly from the choriocapillaris
by diffusion.
Fovea is an avascular area & supplied by
choriocapillaris.
Macular region is supplied by superior & inferior
temporal branch of central retinal artery. Sometimes
cilioretinal artery supplies macula ( branch of ciliary
system). When present, it helps to retain the central

54. Blood Supply Of The Retina
 Retinal vessels are end arteries, usually they do
not form anastomoses. So their occlusion
invariably results into ischemia of the supplied
part.
 Usually normal retinal vessels do not cross
horizontal raphe. Collaterals across midline are a
common finding in retinal venous occlusive
diseases.
 Vessels course in nerve fibre layer & ganglion
cell layer.
 Retinal arteries after 1st branch contains only
endothelial cells & pericytes (1:1). No nerve
fibres are seen in adventitia of the retinal

55. Blood Supply Of The Retina
 VENOUS DRAINAGE:
◦ Usually follows arterial supply. Retinal veins run
parallel to arteries, at places they cross each
other.
◦ At AV-crossings artery is present anterior to the
vein & they share a common adventitial coat. And
this is the reason why AV-crossing changes are seen
during hypertensive retinopathy.
◦ AV-crossings are the most common sites of
branch retinal vein occlusion.
◦ Central retinal vein drains into cavernous sinus so
any infection of eye can travel upto brain by this
route or vice versa.